1. Field of the Invention
The present invention relates to an exothermic device for different electric source for providing constant heat regardless the voltage applied to the exothermal device which is used, e.g., a heat source for evaporating an insecticidal liquid or paste for an electric mosquito-fuge device.
2. Description of the Related Art
In a liquid-type electric mosquito-fuge apparatus as shown in FIG. 5, a ceramic core 3 is inserted in a tank 2 filled with an insecticidal liquid 1, and an exothermic device 4 is fitted on the periphery of the core 3 projected above the tank 2. Electricity is supplied to the exothermic device 4 for heating and the heat is transmitted to the core 3 to evaporate the insecticidal liquid 1 sucked up in the core 3, whereby diffusing the vapour of the insecticidal liquid in a room.
The exothermic device 4 includes a positive temperature coefficient thermistor element 5 as the exotherm element. The positive temperature coefficient thermistor element has a sintered body of a ceramic composition in which the substrate is BaTiO.sub.3 and metal oxides are doped in the substrate. As examples of the positive temperature coefficient thermistor element, there are a thermistor element in which electrodes are formed on both faces of a cylindrical body (Japanese Utility Model Publication No. Hei 1-12395) and a thermistor element in which electrodes are formed on both faces of an arc shaped segment. The exothermic device 4 of the liquid-type electric mosquito-fuge apparatus is normally used by a commercial electric source of 100 V in Japan.
However, the positive temperature coefficient thermistor element incorporated in the exothermic device has such a problem that exothermic temperature varies in proportion to an applied voltage. When 220 V is applied to the exothermic device of a general liquid-type electric mosquito-fuge apparatus, an exothermic temperature rises more than about 7.degree. C. in comparision with the exothermic device to which 100 V is applied.
When the exothermic temperature rises more than 7.degree. C. above a preset temperature, the amount of insecticidal liquid is abnormally evaporated and diffused faster, so that it can not be used for a predetermined effective term of the insecticidal liquid filled in a tank.
In Japan, the voltage of the commercial electric source is unified at AC 100 V. Some countries use AC 220 V as the commercial electric source. Moreover, there are some other countries which use two kinds of voltages for the commercial electric source.
As one example, the commercial electric sources used in the world are shown in the following Table 1. From Table 1, it may be understood that there are many countries which use two kinds of voltages selectively.
TABLE 1 ______________________________________ Area Country (State) Voltage (V) Frequency (Hz) ______________________________________ Asia Japan 100 50/60 China 110/220 50 Hong Kong 200/220 50 India 220 50 Indonesia 127/220 50 Korea 110/220 60 Philippines 110/220 60 Singapore 110/230 50 Taiwan 110 60 Thailand 240 50 North U.S.A. 120 60 America Hawaii 110/120 60 Canada 120/240 60 Central & Argentine 220 50 South Brazile 127/220 60 America Chile 220 50 Mexico 125 60 Peru 220 60 Europe Austria 220 50 Belgium 110/200 50 Denmark 110/220 50 France 127/220 50 Germany 127/220 50 Greece 220 50 Italy 110/220 50 Spain 110/220 50 Sweden 110/220 50 Great Britain 240 50 former USSR 220 50 Africa Kenia 240 50 Oseania Australia 240 50 New Zealand 230 50 ______________________________________
According to Table 1, Korea, the Philippines, Singapore, Belgium, Denmark, Italy, Spain and Sweden use two kinds of voltages, i.e., 110 V and 220 V for the commercial electric source. Therefore, when a positive temperature coefficient thermistor is incorporated in an exothermic device of a mosquitofuge apparatus which is used in these countries, it is necessary to provide a transformer which drops the voltage from 220 V to 110 V of the commercial electric source or to use a transformer to be switched according to the necessity by providing a voltage-switching means to the transformer. To provide the transformer to the apparatus causes the cost-up in manufacturing and increases the weight and volume of the apparatus. Although it has been known that there is an exotherm device which can be used for both AC 110 V and AC 220 V, the purpose of this kind of exothermic the device is merely to improve confidentiality and increase maximum rated voltage. In these exothermic devices, the difference of exothermic temperatures caused by the difference of applied voltages is not considered.
Accordingly, the present invention is to provide an exothermic device which does not cause great degree of exothermic temperature in accodance with the change of an applied voltage.
Another object of the present invention is to provide a positive temperature coefficient thermistor which possesses a region of a current-voltage characteristic as an exothermic device in which a current drops linearly at an angle of about 45.degree. C. in accordance with the increase of an applied voltage.
Another object of the present invention is to provide a positive temperature coefficient thermistor which includes a range of from 100 V to 240 V of applied voltages wherein the voltage-current characteristic is damped linearly at an angle of 45.degree., i.e., which substantially covers the voltage-range of the commercial electric source employed in the countries of the world.
Still another object of the invention is to provide a positive exothermic temperature coefficient thermistor which is formed by a ceramic material composition having BaTiO.sub.3 as a substrate in which the voltage-current characteristic is damped linearly at an angle of 45.degree..